Refactor control plane API spec (#111)
Refactor control plane API spec (#111)

In part of Selector/Recording relationship to better reflect
command responder inner workings. Specifically:

* Add .snmprec file path to the Recording object so that the
  entire file can be operated on together with its location
  under simulator's --data-dir

* Introduce a set of selectors under Agent. Each selector
  holds path to a .snmprec file to use. The path can contain
  templates expandable at run time.

The end result should be roughly the same, as with currently
proposed API model.
etingof/snmpsim,etingof/snmpsim